cerebral aneurisma

7/29/2019 Cerebral Aneurisma

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review article

Th e n e w e n g l a n d j o u r n a l o f m ed i c i n e

n engl j med 355;9 www.nejm.org august 31, 2006928

Medical Progress

Cerebral AneurysmsJonathan L. Brisman, M.D., Joon K. Song, M.D., and David W. Newell, M.D.

From the Department of Cerebrovascularand Endovascular Neurosurgery, New Jer-sey Neuroscience Institute, JFK MedicalCenter, Edison, N.J. (J.L.B.); the Depart-ment of Endovascular Surgery, Institutefor Neurology and Neurosurgery, RooseveltMedical Center, New York (J.K.S.); andthe Department of Neurosurgery, SeattleNeuroscience Institute, Swedish MedicalCenter, Seattle (D.W.N.). Address reprintrequests to Dr. Brisman at the Depart-ment of Cerebrovascular and Endovascu-lar Neurosurgery, New Jersey NeuroscienceInstitute at JFK Medical Center, Edison, NJ08818, or at [email protected].

N Engl J Med 2006;355:928-39.Copyright 2006 Massachusetts Medical Society.

Saccular intracranial aneurysms, abnormal focal outpouch-

ingsof cerebral arteries, cause substantial rates of morbidity and mortality.Recently, major changes have occurred in the way we think about and treat

this disease. Previous concepts about the natural history, particularly the risk ofrupture of certain aneurysms, have been challenged.1,2

When this topic was the subject of a Medical Progress art icle in the Journal in 1997,minimally invasive percutaneous endovascular treatment of intracranial aneurysms(a technique known as coiling) had been introduced as an experimental procedure

for patients who were not good candidates for surgery.3 After almost a decade ofincreased use and evaluation, endovascular coiling has proved to be a safe and

durable alternative to the traditional neurosurgical treatment of craniotomy and clipligation (clipping). Coiling has now surpassed clipping as the primary method

of treatment for intracranial aneurysms in some centers. Since the Guglielmi de-tachable coil for the treatment of intracranial aneurysms was approved in 1995 bythe Food and Drug Administration (FDA), an estimated 150,000 patients have been

treated with this device.4,5 In this article, the technological advances and support-ing research contributing to this important change in practice patterns are re-

viewed.

EPIDEMIOLOGY AND PATHOPHYSIOLOGY

Intracranial aneurysms are common lesions; autopsy studies indicate a prevalencein the adult population between 1 and 5 percent,2 which translates to 10 million to12 million persons in the United States.3 Fortunately, most aneurysms are small,

and an estimated 50 to 80 percent of all aneurysms do not rupture during the courseof a persons lifetime.6 Intracranial aneurysms are considered to be sporadically ac-

quired lesions, although a rare familial form has been described.3 Associated condi-tions include autosomal dominant polycystic kidney disease, fibromuscular dysplasia,Marfans syndrome, EhlersDanlos syndrome type IV, and arteriovenous malfor-

mations of the brain. An estimated 5 to 40 percent of patients with autosomaldominant polycystic kidney disease have intracranial aneurysms,3,7 and 10 to 30

percent of patients have multiple aneurysms.3 Screening with intracranial magneticresonance angiography is indicated for people who have two immediate relatives with

intracranial aneurysms and for all patients with autosomal dominant polycystic kidneydisease.3,8,9 Rescreening of patients with autosomal dominant polycystic kidney dis-ease is recommended, although the frequency of the procedure depends on wheth-

er other affected family members are known to have intracranial aneurysms.8

The estimated incidence of subarachnoid hemorrhage from a ruptured intracra-

nial aneurysm in the United States is 1 case per 10,000 persons, yielding approxi-mately 27,000 new cases of subarachnoid hemorrhage each year.3,5 Subarachnoid

hemorrhage is more common in women than in men (2:1)10; the peak incidence

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n engl j med 355;9 www.nejm.org august 31, 2006 929

is in persons 55 to 60 years old.11 An estimated

5 to 15 percent of cases of stroke are related toruptured intracranial aneurysms.12 Aneurysmal

subarachnoid hemorrhage, a form of hemorrhagicstroke, has a 30-day mortality rate of 45 percent.

An estimated 30 percent of survivors will have

moderate-to-severe disability.13

Little is known about the cause of intracra-

nial aneurysms or the process by which they form,

grow, and rupture, although hypertension and

smoking-induced vascular changes are thoughtto have a major role.3 The most common histo-

logic finding is a decrease in the tunica media,the middle muscular layer of the artery, causing

structural defects. These defects, combined with

hemodynamic factors, lead to aneurysmal out-pouchings at arteria l branch points in the sub-

arachnoid space at the base of the brain (Fig. 1).3

Pericallosal artery, 4%

Anterior communicatingartery, 30%

Internal carotid arterybifurcation, 7.5%

Middle cerebralartery, 20%

Posterior communicatingartery, 25%

Basilar tip, 7%

Posterior inferiorcerebellar artery, 3%

Additional miscellaneous aneurysmlocations not shown: 3.5%

Figure 1. The Intracranial Vasculature, Showing the Most Frequent Locations of Intracranial Aneurysms.

Percentages indicate the incidence of intracranial aneurysms.



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NATURAL HISTORY AND RISK

OF RUPTURE

The most common presentation of intracranial

aneurysm is rupture leading to subarachnoid hem-orrhage.11 At present, aneurysms are increasingly

detected before rupture, given the increased avail-ability and improved sensitivity of noninvasiveimaging techniques. An unruptured aneurysm

may be asymptomatic and thus be found inciden-tally, or it may be diagnosed on the basis of symp-

toms. Unruptured aneurysms cause symptoms byexerting a mass effect, leading to cranial-nervepalsies or brain-stem compression.6 One common

aneurysm-related syndrome is rapid onset of athird-nerve palsy caused by enlargement of an

aneurysm of the posterior communicating artery.3

Aneurysms presenting with subarachnoid hem-

orrhage tend to bleed again. Two to 4 percent

hemorrhage again within the first 24 hours afterthe initial episode, and approximately 15 to 20percent bleed a second time within the first twoweeks.11 Persons with intracranial aneurysms pre-

senting with symptoms of compression such ascranial-nerve palsies or brain-stem dysfunction

should be evaluated and treated promptly becauseof the increased risk of rupture (6 percent per

year)14 in this subgroup.6 The risk of rupture ofan intracranial aneurysm that has not bled but isfound incidentally is much less certain, and these

intracranial aneurysms are generally managedelectively. In the past, unruptured intracranial

aneurysms were viewed as posing a high risk,with an estimated risk of rupture of approximate-

ly 1 to 2 percent per year.15-18 Before the availabil-ity of detachable coils, most intracranial aneurysmswere surgically clipped to prevent rupture.19-21

In 1998, the results of a retrospective study in-volving 53 centers and 2621 subjects challenged

the traditional thinking about the risk of ruptureof unruptured intracranial aneurysms.1 In this

large cohort of people with unruptured aneurysmsselected for conservative treatment, the rate ofrupture for certain small aneurysms (less than

10 mm in diameter) was found to be as low as0.05 percent per year. Among patients with a his-

tory of a bleeding aneurysm, the risk of hemor-rhage was 10 times that of patients who had no

such history. Intracranial aneurysms larger than10 mm and aneurysms of the basilar apex orposterior communicating artery had an even high-

er rate of rupture. The prospective part of the

study (the International Study of Unruptured In-

tracranial Aneurysms), in which 1692 patientsselected for conservative treatment were followed,

yielded similar results. However, the stratif ica-tion was slightly different; the subgroup with the

smallest aneurysms 7 mm or less (which in-

cluded 62 percent of the cohort) had a five-year cumulative rate of rupture of 0 percent.2 A

major objection to that multicenter study is thatthe subjects entered into the study were those

preselected by surgeons for observation on thebasis of their opinion that these aneurysms were

less likely to rupture.22,23 Subsequent studies haveshown higher risks of rupture for unrupturedintracranial aneurysms.24,25

MEDICAL DIAGNOSIS

AND MANAGEMENT

OF SUBAR ACHNOID HEMORRHAGE

Clinical Presentation and Diagnosis

Many patients with subarachnoid hemorrhage

present with an acute onset of severe headache,often described by patients as the worst head-

ache of my life. However, an estimated 10 per-cent die before reaching medical attention, and

many others present in a coma or with severeneurologic compromise.5 Clinical grading scalessuch as the Hunt and Hess Scale (Table 1) are

used to describe the neurologic condition on ad-mission and are considered good predictors of

ultimate outcome.26,27 Computed tomography (CT)

of the head without the administration of contrastmaterial is the initial diagnostic test of choice forsuspected subarachnoid hemorrhage. The Fishergrade uses a four-point scale to describe the

amount of blood on noncontrast-enhanced CT

Table 1. Hunt and Hess Grading Scale for Subarachnoid

Hemorrhage.

Grade Clinical Description

1 Asymptomatic or minimal headache and slightnuchal rigidity

2 Moderate-to-severe headache, nuchal rigidity, andno neurologic deficit other than cranial-nervepalsy

3 Drowsiness, confusion, or mild focal deficit

4 Stupor, moderate-to-severe hemiparesis, andpossibly, early decerebrate rigidity and vege-tative disturbances

5 Deep coma, decerebrate rigidity, and moribundappearance



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of the head and has been shown to correlate with

the development of vasospasm.28 Lumbar punc-ture is reserved for the approximately 5 percent of

patients in whom cranial CT reveals no abnormal-ities, despite a history suggesting a subarachnoid

hemorrhage.11 Bloody cerebrospinal fluid that

fails to clear with continued egress of cerebrospi-nal f luid should raise a suspicion of subarachnoid

hemorrhage. The presence of xanthochromia, ayellowish discoloration of the cerebrospinal fluid

representing bilirubin from the breakdown ofhemoglobin, is even more definitive than a high

red-cell count in the cerebrospinal fluid. Bloodfrom a subarachnoid hemorrhage that occurredmore than 12 hours before the spinal tap will re-

sult in xanthochromic cerebrospinal fluid, where-as fresh blood, as might occur with a traumatic

spinal tap, will not.29

The next step after making a definitive diag-

nosis of a spontaneous subarachnoid hemorrhageshould be to determine whether an aneurysm isthe cause. To do so, it is important to select the

best imaging method for a given patient.

Imaging Methods and Options

The three methods of choice to identify or rule

out an intracranial aneurysm and to delineate thesize and morphologic features of an intracranialaneurysm are CT angiography (CTA) after a ve-

nous injection, magnetic resonance angiography(MRA), and angiography by direct intraarterial

catheterization (catheter angiography); the last is

still considered the benchmark. Several studieshave evaluated the accuracy of detecting intracra-nial aneurysms by comparing CTA, MRA, and thesynergistic combination of CTA and MRA with

catheter angiography, intraoperative findings, orboth.30-35

CTA provides software-generated images fromthin-section contrast-enhanced CT to show cere-

bral vessels in three-dimensional views. The re-constructed pictures, which are obtained in min-

utes, can be rotated and allow the vasculature tobe visualized relative to the brain and the bonesof the skull base, facilitating surgical planning.

Studies evaluating CTA in the management ofintracranial aneurysms have reported sensitivi-

ties ranging from 0.77 to 0.97 and specificitiesranging from 0.87 to 1.00.12,30,31,33,36,37 Sensitivity

drops precipitously for the detection of smalleraneurysms; sensitivity for aneurysms smaller than3 mm is estimated to be 0.40 to 0.91.30,32,38 Cau-

tion must be exercised when CTA is used in pa-

tients with impaired renal function, since a largebolus of contrast material is administered.

MRA takes considerably longer to perform thandoes CTA (roughly 30 to 60 minutes) and is thus

more difficult to use in critically ill patients. MRA

is both highly sensitive and specific for the detec-tion of intracranial aneurysms (sensitivity, 0.69 to

0.99; specificity, 1.00).12,33,36,35 The sensitivity ofMRA, like that of CTA, diminishes for very small

aneurysms (under 3 mm in diameter) and was0.38 in one series.28

In 1998, a three-dimensional form of catheterangiography was developed that permits refor-matted images to be rotated. This advance over

two-dimensional catheter angiography, known asthree-dimensional rotational angiography, per-

mits the aneurysm and its relation to other ves-sels to be assessed in three dimensions, over-

coming prior imaging limitations.39,40 Catheterangiography, with or without the advanced three-dimensional capability, is more expensive and

invasive than either MRA or CTA. Its risks, par-ticularly in the hands of experienced operators,

appear acceptably low (neurologic complicationsoccurring in 1.0 to 2.5 percent of cases, with per-

manent impairment in 0.1 to 0.5 percent),41-44given the seriousness of intracranial aneurysms.Non-neurologic risks such as femoral-artery in-

jury (0.05 to 0.55 percent), groin hematoma (6.9 to10.7 percent), and adverse renal effects induced

by contrast material and other allergic reactions

(1 to 2 percent) are well known and often tran-sient.45 Elderly patients with atherosclerotic ves-sels or patients with impaired renal functionwould be more likely to have complications such

as a thromboembolic event or nephrotoxicity, re-spectively.3

Clinical Approach to Imaging

High-quality catheter angiography is generallydefinitive. Thus, it is the test of choice to evaluate

subarachnoid hemorrhage,12 although CTA alonehas been used.41 Because of the less invasive na-ture of CTA and MRA, they are recommended as

the first approaches in the evaluation of unrup-tured aneurysms.

Angiographic examination fails to disclose ananeurysm in 10 to 20 percent of cases of subarach-

noid hemorrhage. In cases in which the resultsof angiography are negative, angiography is usu-ally repeated in one to six weeks.26,46 The cause



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of a subarachnoid hemorrhage without an iden-

tif ied aneurysm is unknown. Hypertensive rup-ture of a small artery or vein is one proposed

mechanism. In these circumstances, an MRI ofthe brain and cervical spine is usually obtained

after the administration of contrast material dur-

ing the initial admission to rule out a thrombosedaneurysm, hemorrhagic tumor, spinal arteriove-

nous malformation, or dural arteriovenous fis-tula, although the diagnostic yield is small.

Acute Effects of Subarachnoid Hemorrhage

Hydrocephalus develops in about 15 to 20 percentof patients who have an aneurysmal subarach-noid hemorrhage.11 Symptomatic hydrocephalus

is usually treated with ventriculostomy and drain-age of cerebrospinal f luid.

Cerebral vasospasm, a major cause of morbid-ity and mortality, refers to the intracranial vaso-

constriction that may occur between 3 and 12days after a subarachnoid hemorrhage. The causeof vasospasm is unknown; even with maximal

therapy, vasospasm can cause strokes and death.11Transcranial Doppler ultrasonography is a useful

noninvasive method to detect vasospasm.

Medical Therapy

Medical treatment consists of orally administerednimodipine (60 mg every four hours for 21 days),

which has been shown to improve the outcomeafter subarachnoid hemorrhage.47 In patients who

have a clear increase in the transcranial Doppler

velocities or in whom new neurologic deficits de-velop, triple-H (hypertension, hypervolemia, andhemodilution) therapy is initiated. Goals of thistreatment include a hematocrit of 30 percent, a

central venous pressure of 8 to 12 mm Hg, andenough artificially induced hypertension to pre-

vent or reverse new neurologic deficits.5,11,26 Suchdeficits usually correlate with the vascular terri-

tory of the vessel in spasm and may be as subtle asa decrease in the level of arousal or as overt as a

new hemiparesis. In light of the risks of triple-Htherapy, such as cardiac dysfunction, catheter an-giography is occasionally used to confirm the

findings on transcranial Doppler examination.Patients with any persistent new neurologic

deficit who have no response to medical treatmentshould undergo urgent catheter angiography to

confirm the presence of vasospasm, followed byangioplasty of the narrowed vessels or intraarte-rial administration of smooth-muscle relaxants

such as papaverine.48,49 Balloon angioplasty and

antispasmodic agents result in angiographicallyconfirmed arterial dilatation in a high percent-

age of patients (90 to 98 percent).49,50 Clinicalimprovement, however, does not invariably cor-

relate with radiographic success. Some observers

report a rate of neurologic improvement of 61 to70 percent, whereas others report no benefit as

compared with triple-H therapy.49,51,52

Evidence of cardiac abnormalities after sub-

arachnoid hemorrhage is common and includeselectrocardiographic changes (25 to 100 percent

of cases),53,54 elevations of cardiac enzymes (tro-ponin in 17 to 28 percent and creatine kinaseMB isoenzyme in 37 percent of cases),53,55-57 and

left ventricular dysfunction (8 to 30 percent ofcases).58,59 This combination of abnormalities,

known as cardiac stun, appears to result fromexcessive catecholamine release in response to

the intracranial hemorrhage. The presence of amarkedly decreased ejection fraction with motionabnormalities of the ventricular wall that do not

match the electrocardiographic vascular distribu-tion of ischemia helps to make the diagnosis.56,59

Levels of both creatine kinase MB isoenzyme andtroponin are usually elevated, but the troponin

elevation is generally only a 10th of that seenwith true ischemic myocardium.56 Most cases ofcardiac stun are temporary; permanent myocardial

injury appears to be rare, irrespective of whetherearly treatment of the aneurysm is performed.53

TREATMENT OPTIONS

There are three options for treating intracranialaneurysms: observation, craniotomy with clip liga-

tion (clipping) (Fig. 2), and endovascular occlu-sion with the use of detachable coils (coiling)

(Fig. 3). All ruptured aneurysms in patients withHunt and Hess grades 1 to 4 are treated early

(generally within 72 hours). There is debate abouthow to treat patients with the most severe grade,

Hunt and Hess grade 5; the historically high in-cidence of poor outcome despite treatment hasprompted the suggestion of conservative manage-

ment unless clinical improvement occurs. How-ever, recent evidence supports the use of aggres-

sive therapy for most of these patients, includingplacement of a ventricular drain and securing the

aneurysm by clipping or coiling.26 Detachable coilshave been increasingly used as a less physiologi-cally stressful alternative to clipping the aneurysm



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in this subgroup of patients, who already have se-

vere brain injury.26

Intact aneurysms that are discovered inciden-

tally are either observed or treated electively, de-pending on the patient and the size and state of

the aneurysm. Observation consists of routine pe-

riodic follow-up imaging and physician visits toreview the studies. Clipping of aneurysms requires

the performance of a craniotomy by a neurosur-geon with the patient under general anesthesia.

Permanent clips made from MRI-compatible al-loys are placed across the neck of the aneurysm,

excluding it from the circulation (Fig. 2).

An interventional neuroradiologist, a neuro-surgeon, or a neurologist with training in inter-

ventional radiology performs endovascular coil-ing.60 General anesthesia is often used during the

placement of detachable coils, although some cen-ters prefer to use only sedation in order to moni-

tor the patients neurologic status during the pro-cedure.61 Neurophysiological monitoring has beendescribed as another way to monitor neurologic

function during coiling.62 With the use of angio-graphic techniques, a microcatheter is advanced

into the aneurysm, and detachable coils of vari-ous sizes and shapes are deployed to decrease the

amount of blood or to stop blood from filling theaneurysm (Fig. 3).

COMPARIson of CLIPPING AND COILING

Risks of Clipping

In one large, single-center series and two meta-

analyses, the morbidity and mortality rates associ-ated with clipping an unruptured aneurysm rangedfrom 4.0 to 10.9 percent and 1.0 to 3.0 percent,respectively.19-21 Although successful clipping is

generally associated with definitive protectionagainst rupture, long-term studies have document-

ed a certain small risk of technical failure, incom-plete occlusion (5.2 percent),63 recurrence (1.5 per-

cent), and hemorrhage (0.26 percent).64

The International Study of Unruptured Intra-

cranial Aneurysms assessed the risk of morbid-ity associated with the clipping of unrupturedaneurysms. The risk associated with surgical re-

pair was reported to be 15.7 percent after oneyear, higher than previously reported.1 Additional

single-center reports, however, have since dem-onstrated a lower risk of surgical morbidity, in

the range of 3 to 7 percent.6 In any event, the re-sults of the International Study of UnrupturedIntracranial Aneurysms have had an important

effect on the management of unruptured aneu-rysms65,66; more aneurysms are now treated with

observation. Guidelines for the management ofunruptured intracranial aneurysms were issuedby the Stroke Council of the American Heart As-

sociation in 2000.12

Risks of Inserting Detachable CoilsMinor risks of inserting detachable coils, such as

reactions to contrast material and groin hemato-mas, infections, or pseudoaneurysms, are similarto those of diagnostic catheter angiography.67 Ma-

Skin incision

Craniotomysegment

Clip applied toneck of aneurysm

Aneurysm

A

B

Figure 2. Microsurgical Clipping of an Aneurysm of the Posterior Communi-

cating Artery.

Panel A shows the typical skin incision (unbroken curved line) and craniotomy

(dashed lines) needed to access the aneurysm. Panel B shows the applicationof the clip blade to the neck of the aneurysm.



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jor risks include arterial dissection (0.7 percent),parent-artery occlusion (2.0 percent), and throm-

boembolic phenomena (2.4 percent).68 Intrapro-cedural rupture of the aneurysm during catheteradvancement into the aneurysm or coil place-

ment is one of the most serious complications;two large series and one meta-analysis cited an

incidence of 1.4 to 2.7 percent, with an associat-ed mortality rate of 30 to 40 percent.68-70 Evenlower rates of intraprocedural rupture (1 percent)

Catheter

Coil

Microcatheter

Aneurysm

A

B

Coil in place

Figure 3. Endovascular Occlusion of an Aneurysm of the Posterior Communicating Artery with Guglielmi Detachable Coils.

Panel A and inset show the route of the microcatheter into the aneurysm through the right femoral artery, aorta, and left carotid artery

and the beginning of the coil deployment. Panel B shows the final occlusion of the aneurysm with coils.



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have recently been reported in one high-volume

center; in that report, the associated morbiditywas low (17 percent) and the mortality rate was

0 percent, perhaps reflecting increasing familiar-ity and experience with coils after approval by the

FDA in 1995.71 Overall procedural morbidity and

mortality rates for coiling have been reported as3.7 to 5.3 percent and 1.1 to 1.5 percent, respec-

tively.72,73 It is not feasible to perform a coilingprocedure for some aneurysms (5 to 14.5 percent

of cases),68,74 because unusual tortuosity of thevessels renders access difficult or because the con-

tours of the aneurysm do not permit the coils tosit safely inside.

Recent technologic advances, including coils

that are better able to conform in aneurysms withatypical morphology, balloons,75 and intracranial

stents, which were introduced in 2002 (Fig. 4),76,77have markedly reduced the number of aneurysms

that cannot be approached with the detachable-coil procedure. Importantly, there is a greaterlikelihood of partial occlusion when coils are

used than when surgical clipping is used. In threesingle-center studies, 2868 subjects with intra-

cranial aneurysms underwent a coiling proce-dure; successful angiographic occlusion (defined

as >90 to 95 percent occlusion or a neck remnantonly) was achieved in 85 to 90.4 percent of le-sions. Larger aneurysms and aneurysms with

wider necks typically had lower rates of success-ful occlusion.68,72,78

Aneurysms that have been treated with coils

may recur, and with recurrence, they have thepotential to hemorrhage. Over time, blood flowcan compress the coils within the aneurysm, aprocess known as compaction; as a result, the

aneurysm may refill with blood, a process referredto as recurrence, or recanalization (Fig. 4). Re-

canalization rates appear to be in the range of20.9 to 33.6 percent.79 The importance of recur-

rence is unknown; also unknown is whether apartially coiled aneurysm is protected. Vigilant

follow-up angiography is needed to detect aneu-rysms that recanalize,78,79 since re-coiling may beindicated and is safe (there were no complications

in 53 aneurysms that underwent re-coiling in onestudy).80 The risk of hemorrhage from a coiled

aneurysm is thus higher than after confirmedclip ligation, but it is still very small; one large

study documented a risk of 0.8 percent, with amean (SD) follow-up of 31.3224.96 months.79

A promising solution to the problem of recur-

rence after coiling is the advent of biologically ac-

tive coils that are impregnated with substancesintended to interface with the vessel endothelium

and form a collagenous matrix at the entrance ofthe aneurysm.81 Another new type of coil77,82 that

expands once inside the aneurysm to induce

denser packing appears to reduce the incidenceof coil compaction in animal models.83 Another

potential solution to recanalization is a new flex-ible, self-expandable, microcatheter-delivered, ni-

tinol stent (Neuroform stent, Target Therapeutics/Boston Scientific) (Fig. 4). This intracranial stent,

which was recently approved by the FDA, is placedwithin the artery from which the aneurysm arises,thereby blocking it.76,77

Relative Risks of Coiling and Clipping

Several retrospective studies84-86 suggest that de-spite its attendant risks, treating most ruptured

and unruptured intracranial aneurysms with de-tachable coils appears to be safer than clipping,at least during the perioperative period. In sepa-

rate reviews of a database of a university healthsystem consortium (60 universities),86 the Califor-

nia statewide database of hospital discharges,85and the hospital database of the University of

California at San Francisco,84 Johnston et al. re-ported that outcomes associated with clippingwere worse than those associated with detach-

able coils. They also reported that the use of coilswas associated with a lower rate of inpatient mor-

tality, shorter hospital stay, and lower treatment

costs.84-86

More robust data favoring the safety of coil-ing over clipping are available for aneurysms pre-senting with subarachnoid hemorrhage from a

large, multicenter prospective study conductedin England.87 In the International Subarachnoid

Aneurysm Trial, 2143 patients presenting with aruptured aneurysm were prospectively randomly

assigned to either clipping or coiling.88 A plannedinterim analysis of the data-monitoring commit-

tee indicated a rate of 23.7 percent for neurologicincapacity (dependency) or death in the endovas-cular cohort, as compared with 30.6 percent in

the surgical group; recruitment into the trial wasimmediately stopped, since the relative risk (22.6

percent) and the absolute risk (6.9 percent) ofdependency and death in the group assigned to

coiling was clearly reduced as compared withthat in the group assigned to clipping. These ob-servations were upheld in the one-year follow-up



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report on the patients who had been recruited

and treated before the trial was stopped.88

The results of this trial have had an important

and lasting impact on the treatment of intracra-nial aneurysms.89,90 The American Society of In-

terventional and Therapeutic Neuroradiology91and the American Association of Neurological

Surgeons92 have responded to and critiqued thestudy in position statements, and the change inpractice patterns engendered by the study has

been reported.89,90 Several caveats, however, areworth noting. The study assessed 9559 patients

with aneurysmal subarachnoid hemorrhage, butonly a fraction of these patients were considered

candidates equally suitable for clipping or coiling(inclusion criteria); thus, only 2143 patients (22.4percent) underwent randomization. In addition,

most of the patients presented with a favorable

clinical grade (>90 percent) and had aneurysmsin the anterior circulation (97.3 percent) that were

smaller than 10 mm (nearly 95 percent). Gener-alizing these findings to all intracranial aneu-

rysms is not appropriate. Given the findings of theInternational Subarachnoid Aneurysm Trial, the

American Society of Interventional and Therapeu-tic Neuroradiology recommends that all patientswith ruptured intracranial aneurysms undergo

independent evaluation and counseling by a physi-cian capable of performing a detachable-coil pro-

cedure for aneurysms.91 The position statementof the American Association of Neurological Sur-

geons recommends surgical clipping as the treat-ment of choice, if an experienced vascular neuro-surgeon believes it to be the best option.92

Coil

Aneurysm

Stent

Microcatheter

A

D

B

E

C

F

Aneurysm

Figure 4. Stent-Assisted Re-Coiling after Recurrence of an Aneurysm Initially Treated with Coiling.

Panel A (three-dimensional rotational catheter angiogram) and Panel B (left carotid injection, two-dimensional catheter angiogram,oblique view) show an aneurysm of the posterior communicating artery (Panel B, arrow). Panel C (two-dimensional catheter angiogram,

lateral view) shows the successful coiling of the aneurysm (arrow); this was followed eight months later with marked coil compaction and

recanalization of the aneurysm (Panel D, two-dimensional catheter angiogram, lateral view). Panel E (two-dimensional catheter angio-

gram, lateral view) shows successful re-coiling of the aneurysm with the assistance of a stent (too small to visualize). Panel F shows the

configuration used for the stent and the coil.



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The Effects of Surgeon and Hospital Volume

Studies examining the outcomes of treatment ofaneurysms as related to the experience of a par-

ticular surgeon, interventional radiologist, or in-stitution indicate better outcomes when a high

volume of procedures is performed.93-96 Most of

these reports have been published by institutionsand surgeons who have performed a high volumeof procedures. One study reported better outcomeswith surgeons who performed more than 30 cra-

niotomies for aneurysms per year.97 Such studieshave prompted some observers to recommend re-

gionalization of care for intracranial aneurysms.

Optimal Treatment of Aneurysms

The optimal management of both ruptured andunruptured intracranial aneurysms has not been

fully determined. On the basis of the literature, itis important to consider the factors that support

the treatment of an intracranial aneurysm witheither surgical clipping or placement of detach-

able coils. In some cases either method is appro-priate, and the decision may be influenced bydiff icult-to-quantif y variables such as patient pref-

erence or operator availability or expertise.

Whether a given intracranial aneurysm should

be observed, treated surgically, or managed endo-vascularly remains controversial. Ruptured intra-

cranial aneurysms should be treated in a timelyfashion to prevent a disastrous recurrence of hem-

orrhage; increasingly, the data support the use of

coiling as a less invasive method for this purpose.Intracranial aneurysms that are incidentally discov-

ered need not be treated in certain patients. Wheth-er the increased durability afforded by clipping

outweighs its slightly higher risks, as comparedwith those of coiling, remains to be determined.

Endovascular technology, despite its currentlimitations, is likely to continue to advance ourability to treat intracranial aneurysms. Both on-

going clinical trials, such as the International Sub-arachnoid Aneurysm Trial and the International

Study of Unruptured Intracranial Aneurysms, andfuture randomized trials comparing clipping and

coiling should shed light on the natural historyof intracranial aneurysms along with the relativerisks and benefits of observation as compared

with interventions such as coiling and clipping.

No potential conflict of interest relevant to this article wasreported.

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